1. Field of the Invention
The present invention relates in general to semiconductor manufacturing, and particularly to formation of a patterned photoresist layer by photolithography.
2. Description of the Related Art
As semiconductor manufacturers have sought to fabricate devices with a higher degree of circuit integration to improve device performance, it has become necessary to use photolithographys with shorter wavelengths in the mid and deep UV spectra to achieve fine features. In the process of making the desired very fine patterns, many optical effects are experienced which lead to distortion or displacement of images in the photoresist that are directly responsible for wiring line width variations, opens and shorts, all of which can lead to deteriorated device performance. Many of these optical effects are attributable to substrate geometry and reflectivity influences that include halation and other reflected light scattering effects which may occur due to uneven topography or the varying (wavelength dependent) reflectivity of the substrates and wires or layers being patterned thereon to define the desired features. Such effects are further exacerbated by both the non-uniformity of the photoresist film and film thickness. These effects are manifested in lithographic patterns uneven line width, often with “reflective notching”, due to standing wave phenomena, and non-vertical pattern side walls.
One way to solve standing wave phenomena is the application of anti-reflection coating (ARC). An anti-reflection coating is formed on a substrate to impede reflection of the light source.
Post-exposure baking (PEB) of the photoresist layer before development process is another way to solve standing wave phenomena. The structure of the photoresist layer is rearranged, thereby, standing wave phenomena are alleviated.
In traditional photolithography, a bake is usually performed twice to improve the profiles of the patterned photoresist layer. However, the baking temperature adversely affects the profiles thereof. If the structure of the photoresist layer is not dense enough, an undercut problem will occur when the baking temperature is too low. If the structure of the photoresist layer is too dense, a footing problem will occur when the baking temperature is too high.
Prior-art photolithography is shown in FIG. 1A to FIG. 1D.
In FIG. 1A, a substrate 101 is provided. An anti-reflection coating layer 102 is preferably formed on the substrate 101 by spin coating. A bake is then performed to strengthen the structure of the anti-reflection coating layer 102.
In FIG. 1B, a photoresist layer 103 is preferably formed on the anti-reflection coating layer 102 by spin coating. Exposure is then performed using a selected mask to transfer the mask patterns to the photoresist layer 103. Next, a post-exposure bake is performed.
In FIG. 1C, development is performed to form a patterned photoresist layer.
However, an undercut 104a and a footing 104b occur in the patterned photoresist layer in accordance with traditional photolithography, as shown in FIG. 1C.